CA-322 Chapter 12 . Area of Shapes SECTION 12.8 CLASS ACTIVITY 12-R X Critique Reasoning about Perimeter CCSS COSS SMP3, 3.MD.8 Materials You will need a centimeter ruler for part 2. 1. Johnny's method for calculating the perimeter of the shaded shape in Figure (a) is to shade the squares along the border of the shape, as shown in Figure (b), and to count these border squares. Therefore, Johnny says the perimeter of the shape is 24 units. Is Johnny's method valid? If not, why not? (a) (b 2. When Susie was asked to draw a shape with perimeter 15 cm, she drew a shape like the shaded one shown in the figure below on centimeter grid paper. a. Carefully measure the diagonal line segment in the shaded shape with a centimeter ruler. Then explain why the shape does not have perimeter 15 cm. b. Draw a shape that has perimeter 15 cm on the same graph paper. (The vertices of your shape do not have to be located where grid lines meet.) Explain how you figured out how to make your shape